The study of electrostatics has proven useful in many areas. This module covers just a few of the many applications of electrostatics. Van de Graaff generator s or Van de Graaffs are not only spectacular devices used to demonstrate high voltage due to static electricity—they are also used for serious research. The first was built by Robert Van de Graaff in based on original suggestions by Lord Kelvin for use in nuclear physics research.
Van de Graaffs use both smooth and pointed surfaces, and conductors and insulators to generate large static charges and, hence, large voltages.
A very large excess charge can be deposited on the sphere because it moves quickly to the outer surface. Practical limits arise because the large electric fields polarize and eventually ionize surrounding materials, creating free charges that neutralize excess charge or allow it to escape.
Nevertheless, voltages of 15 million volts are well within practical limits. Most copy machines use an electrostatic process called xerography —a word coined from the Greek words xeros for dry and graphos for writing. A selenium-coated aluminum drum is sprayed with positive charge from points on a device called a corotron. Selenium is a substance with an interesting property—it is a photoconductor.
That is, selenium is an insulator when in the dark and a conductor when exposed to light. In the first stage of the xerography process, the conducting aluminum drum is grounded so that a negative charge is induced under the thin layer of uniformly positively charged selenium.
In the second stage, the surface of the drum is exposed to the image of whatever is to be copied. In locations where the image is light, the selenium becomes conducting, and the positive charge is neutralized. In dark areas, the positive charge remains, so the image has been transferred to the drum. The third stage takes a dry black powder, called toner, and sprays it with a negative charge so that it is attracted to the positive regions of the drum.
Next, a blank piece of paper is given a greater positive charge than on the drum so that it will pull the toner from the drum. Finally, the paper and electrostatically held toner are passed through heated pressure rollers, which melt and permanently adhere the toner to the fibers of the paper. In its most common application, the laser printer receives output from a computer, and it can achieve high-quality output because of the precision with which laser light can be controlled.
Many laser printers do significant information processing, such as making sophisticated letters or fonts, and in the past may have contained a computer more powerful than the one giving them the raw data to be printed.
The ink jet printercommonly used to print computer-generated text and graphics, also employs electrostatics. Once charged, the droplets can be directed, using pairs of charged plates, with great precision to form letters and images on paper.
Ink jet printers can produce color images by using a black jet and three other jets with primary colors, usually cyan, magenta, and yellow, much as a color television produces color. This is more difficult with xerography, requiring multiple drums and toners. Electrostatic painting employs electrostatic charge to spray paint onto oddly shaped surfaces.
Mutual repulsion of like charges causes the paint to fly away from its source. Surface tension forms drops, which are then attracted by unlike charges to the surface to be painted.
Electrostatic painting can reach hard-to-get-to places, applying an even coat in a controlled manner. If the object is a conductor, the electric field is perpendicular to the surface, tending to bring the drops in perpendicularly.
Corners and points on conductors will receive extra paint. Felt can similarly be applied. Another important application of electrostatics is found in air cleaners, both large and small. Home precipitators, often in conjunction with the home heating and air conditioning system, are very effective in removing polluting particles, irritants, and allergens.Electrostatic force is the phenomenon that results from slow-moving or stationary electrical charges.
It is studied in the scientific discipline known as electrostatics by researchers analyzing electromagnetic interaction. Specifically, electrostatic force is the physical reaction that holds together the electromagnetic field created by subatomic particles, such as electrons and protons. In order for electrostatic forces to remain cohesive, these particles need to independently maintain both positive and negative charges and react to each other accordingly.
According to the laws of physicsthere are four fundamental forces that describe the reactions of particles, one of which is considered electromagnetic forcewhich results in electrostatic force under certain conditions. Electrostatic force between electrons and protons is one of the strongest forces in the universe, even more powerful than gravity.
A hydrogen atom, which contains only one electron and one protonhas the fundamental force of gravity keeping it together. However, each subatomic particle can develop electrostatic force as well, which becomes even stronger.
In physics, the laws state that a magnitude of force must be exerted between the particles that is 10 24 stronger than simple gravity. Each atom in the universe in its natural state contains an even amount of protons and electrons, creating a strong presence of electrostatic forces. As two surfaces come in contact with each other, charge exchange occurs, resulting in the development of electrostatic forces.
When resistance is present in one of these materials, electrostatic charges are more apparent to the observer. The resistive material retains the electrostatic charge for a longer period of time until the charges become neutralized, such as with a static shock. Coulomb 's law defines the fundamental theories regarding electrostatic force of attraction within the science of electrostatics.
It was established in the s by a French physicist named Charles Augustin de Coulomb. He utilized the basic theories of electromagnetism to determine the formulas and equations that defined electromagnetic forces and electrostatics. One of the most common examples of electrostatic force seen in everyday life occurs when someone opens up a plastic package.
Often, this package becomes stuck to one's fingers. This is due to the fact that the package, containing electrically-resistant properties, had rubbed against other surfaces, building up an electrostatic charge.
The ancient Greeks were the first to notice this concept when they researched amber. Amber possesses the ability to attract particles when rubbed with a another material. Jason C. Chavis Last Modified Date: September 25, Please enter the following code:. Login: Forgot password?The method of image charges also known as the method of images and method of mirror charges is a basic problem-solving tool in electrostatics.
7.7: Applications of Electrostatics
The name originates from the replacement of certain elements in the original layout with imaginary charges, which replicates the boundary conditions of the problem see Dirichlet boundary conditions or Neumann boundary conditions.
The validity of the method of image charges rests upon a corollary of the uniqueness theoremwhich states that the electric potential in a volume V is uniquely determined if both the charge density throughout the region and the value of the electric potential on all boundaries are specified. Possessing knowledge of either the electric potential or the electric field and the corresponding boundary conditions we can swap the charge distribution we are considering for one with a configuration that is easier to analyze, so long as it satisfies Poisson's equation in the region of interest and assumes the correct values at the boundaries.
This situation is equivalent to the original setup, and so the force on the real charge can now be calculated with Coulomb's law between two point charges. The surface charge density on the grounded plane is therefore given by. In addition, the total charge induced on the conducting plane will be the integral of the charge density over the entire plane, so:.
The total charge induced on the plane turns out to be simply —q. This can also be seen from the Gauss's lawconsidering that the dipole field decreases at the cube of the distance at large distances, and the therefore total flux of the field though an infinitely large sphere vanishes. Because electric fields satisfy the superposition principlea conducting plane below multiple point charges can be replaced by the mirror images of each of the charges individually, with no other modifications necessary.
The dipole experiences a force in the z direction, given by. Similar to the conducting plane, the case of a planar interface between two different dielectric media can be considered. It can be shown that the resulting electric field inside the dielectric containing the particle is modified in a way that can be described by an image charge inside the other dielectric.
Inside the other dielectric, however, the image charge is not present. It may even have the same sign, if the charge is placed inside the stronger dielectric material charges are repelled away from regions of lower dielectric constant.
This can be seen from the formula. The method of images may be applied to a sphere as well. In the figure, this is represented by the green point. Let q be the charge of this point. The image of this charge with respect to the grounded sphere is shown in red.
The potential inside the sphere is thus given by the above expression for the potential of the two charges. The potential outside the grounded sphere will be determined only by the distribution of charge outside the sphere and will be independent of the charge distribution inside the sphere.
Note that the reciprocal problem is also solved by this method. The potential inside the sphere will be dependent only upon the true charge distribution inside the sphere.These are the world class predictions given by cricket experts based on facts and figures of team players and their previous performance.
India Vs Srilanka 1st ODI Today Match Prediction 10 December Sunday 2017. Who Will Win Ind Vs Sri 1st ODI match.
What is an Electrostatic Force?
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If fertility rates, the size of youth populations, and rates of religion switching remain the same, Christianity will still be the largest religion in the world in 2050, according to a detailed report released today by the Pew Research Center. But Islam will be gaining fast, nearly neck-and-neck with Christianity "possibly for the first time in history," and potentially eclipsing Christianity after 2070.
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Method of image charges
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